The present invention relates generally to chain-driven or to belt-driven mechanisms, and in particular to tensioning devices therefor.
A typical chain-driven mechanism includes a driver sprocket and a driven sprocket interconnected by a linked chain. The interconnecting chain desirably remains at a selected tension during operation. In some cases, the driver sprocket and driven sprocket remain at a fixed relative separation. In such cases, the length of the chain relative to the fixed separation between and the driver sprocket and driven sprocket establishes the desired chain tension. As the chain wears, however, tension diminishes and eventually becomes unacceptable. In other cases, spring biased tensioning devices attach to surrounding frames or structures of the chain-driven mechanism. Typically, such frame-mounted tensioning devices are part of the design of the mechanism as provided by the original manufacturer, i.e., as an integral and essential part of device operation. As the chain wears or becomes loose, such frame-mounted tensioning devices maintain the selected tension in the chain for ongoing reliable operation.
Unfortunately, not all chain-driven mechanisms come with a chain tensioner or have available surrounding frames or structures to support a spring-biased tensioning device. In many cases, the drive sprocket and driven sprocket are separated at fixed distance without any appropriate intervening structure. Chain tension is established only by careful selection of chain length in relation to fixed separation between the driven sprocket and driver sprockets. In such arrangements, chain wear eventually produces loss of chain tension. With no opportunity to reposition either one of the driver sprocket or driven sprocket, chain replacement is an expensive option. Where the driver sprocket and driven sprocket may be adjusted in position relative to one another, chain tension may be adjusted by virtue of such repositioning capability. Many times, however, such repositioning of the driver or driven sprocket is inconvenient or lacks the necessary range of adjustment needed to maintain sufficient chain tension.
Floating chain tensioners provide a mechanism maintaining tension in a chain-driven system without requiring attachments to any surrounding structures or re-positioning of the sprockets. Accordingly, floating chain tensioners find great utility in machines with no surrounding supporting frame suitable for mounting a tensioning device; in machines in which the original manufacturer did not provide a tensioning mechanism; and in cases where the user is simply unwilling to go to the expense or trouble of mounting some form of tensioning device relative to surrounding frame work. The floating tensioning device provides a quick and ready solution in the above-noted situations and in other situations where chain tension is required in a chain-driven system.
Floating chain tensioners typically include a pair of chain-engaging members, e.g., slide blocks or sprockets, maintained at a selected fixed distance during operation and bearing against the chain to establish chain tension. More particularly, such chain-engaging members typically bear against the upward-facing portion of an upper section of chain and a downward-facing portion of a lower section of chain to force the chain into an "hour-glass" shape. Some chain tensioners provide adjustment in relative position between the chain-engaging members, but during operation maintain such chain-engaging members at fixed separation. Accordingly, as the chain wears, the chain tensioner eventually cannot maintain tension and frequent adjustments, i.e., in relative position between the chain-engaging members, are necessary. Furthermore, such chain tensioning devices with chain-engaging members at fixed separation cannot continuously maintain the desired chain tension through the dynamic conditions of machine operation. The chain is never maintained in control at the necessary tension and the chain and floating chain tensioner tend to jump about significantly during operation. Because such chain tensioners, i.e., chain tensioners with fixed separation between chain-engaging members, cannot maintain optimum chain tension through dynamic operating conditions, such chain tensioners cannot satisfactorily maintain chain tension for all conditions, e.g., during start-up, normal operation, light loading, heavy loading, slow down, or stop conditions.
U.S. Pat. No. 5,000,724 issued Mar. 19, 1991 and entitled Roller Chain Tensioning Device shows a floating chain tensioning device including a pair of low friction chain-engaging blocks held at a selected distance and against a roller chain by means of a strap and fastener device. The strap loops through the chain-engaging blocks and pulls the blocks together to capture the roller chain therebetween and establish tension therein. Once tightened by means of the strap and fastener device, the woven nylon straps maintain the chain-engaging blocks at a selected distance apart to induce a selected tension in the roller chain.
U.S. Pat. No. 4,798,562 issued Jan. 17, 1999 and entitled Tensioning Device for Flexible Drive Element illustrates a similar floating chain tensioner with brackets maintaining chain-engaging blocks at a selected distance to bear against a chain therebetween and establish tension therein. While the device allows selected separation, i.e., adjustment, between the chain-engaging blocks, the blocks remain at a fixed relative distance during machine operation. U.S. Pat. No. 4,662,862 issued May 5, 1987 and entitled Tensioning Device for a Flexible Drive Element shows a similar floating chain tensioning device employing a ratchet mechanism, but during operation maintaining a fixed distance between the chain-engaging blocks. U.S. Pat. No. 4,850,934 issued Jul. 25, 1999 and entitled Stabilized Tensioning Device for Flexible Drive Element also shows a floating tensioning device having adjustable separation between chain-engaging blocks but fixed separation during operation thereof.
U.S. Pat. No. 3,630,096 issued Dec. 28, 1971 and entitled Drive-Tensioning Apparatus discloses a device including a pair of rotatable sprockets carried upon a floating arm and maintained at fixed distance therebetween. The floating arm slides within a frame-mounted bracket. During operation, the floating arm moves in response to chain tensioning conditions, but the sprockets remain at all times at a fixed distance therebetween.
U.S. Pat. No. 1,338,405 issued Apr. 27, 1920 and entitled Belt Tightener shows a pair of pulleys mounted rotatably upon a pair of supporting brackets adjustable in length to establish a selected distance between the pulleys for capturing a belt therebetween and establishing tension therein.
U.S. Pat. No. 3,941,006 issued Mar. 2, 1976 and entitled Free Floating Belt Tensioner illustrates a pair of pulleys rotatably mounted upon a Z-shaped bar including length adjustment therealong to establish a selected separation between the pulleys and capture a belt therebetween.
U.S. Pat. No. 3,926,063 issued Dec. 16, 1975 and entitled Floating Idler Pulley Apparatus shows a belt tensioning device including a pair of pulleys bearing against and capturing a belt therebetween to establish tension therein. The tensioning pulleys are adjustable in position, but during operation remain at a fixed distance therebetween. While adjustment in position is contemplated during operation, such adjustment must be done manually and absent such adjustment the pulleys remain at fixed separation during normal operation of the device.
Thus, floating tensioners find use in a variety of applications, especially when the drive and driven sprockets are in fixed positions relative to one another, when one wishes to extend the life of a wearing chain by maintaining tension therein, and anytime one wishes to avoid the trouble and expense of establishing a mounting site for a frame-mounted tensioning device especially in a mechanism where the original manufacturer did not provide such tensioning device. The subject matter of the present invention addresses these issues by improving floating tensioners.